APPARATUS AND METHOD FOR MOVING A DIE OF A PRESSURE DIE CASTING MACHINE

Abstract: The invention relates to pressure die casting machines, and in particular to an apparatus and method for moving a die of a pressure die casting machine. According to the invention, there is provided a die casting machine having a machine base; first and second platens (10, 12) fixed to the machine base; a third platen (14) movable relative to the machine base, and positioned between the first and second said platens; at least two tie bars (22, 23), the third platen being slidably mounted on said tie bars; a protuberance (21) on each said tie bar; tie bar hydraulic cylinders (20) connected to the third platen; at least two guide bars (32) projecting through the third platen, each said guide bar having a guide bar protuberance (31); guide bar hydraulic cylinders (30) connected to the third platen, each of the cylinders (20, 30) being slidable sealingly upon respective protuberance whereby said protuberance forms a stationary piston defining first and second hydraulic chambers (25, 26, 35, 36) within the movable hydraulic cylinder; and first and second hydraulic conduit means (27, 37, 54, 55) connected respectively to the first and second hydraulic cylinder chambers for movement of the cylinder and thus of the third platen in opposite respective directions; each tie bar being fixed both to the first and second platens, each guide bar being fixed only to the first platen and not to the second platen.

Description: APPARATUS AND METHOD FOR MOVING A DIE OF A PRESSURE DIE CASTING MACHINE FIELD OF THE INVENTION This invention relates to pressure die casting machines, and in particular to an apparatus and method for moving a die of a pressure die casting machine. BACKGROUND TO THE INVENTION Pressure die casting is the injection of molten metal or plastic under high pressure into a mould cavity. For simplicity, the following description concerns apparatus and method to produce metal castings; the apparatus and method to form plastics castings is similar. Prior to injection of the molten metal into the cavity, the mould is "closed" i.e. the two halves of the mould, called dies, are brought together; thereafter the dies are held together whilst the molten metal is forced into the cavity they form. The metal is allowed to solidify, to the shape of the mould cavity; and then the dies are pulled apart so that the solidified object can be ejected and the cycle repeated. To produce die castings free from pores and shrink holes it is standard practice to fill the mould at high pressure, and to allow the metal to solidify whilst under the high pressure, whereby to effect compression of the metal of the die casting. The apparatus for closing the dies and for holding the dies together needs to be able to withstand this high pressure, and to continue working for long periods. To simplify the clamping arrangement for holding the dies together, known apparatus utilises a die casting machine which has one die fixed relative to the machine and a second die which is movable into and out of engagement therewith. Thus the movement and control apparatus can be provided for the second die only; this has the further advantage that the hot melt can (subsequently) be fed into the mould cavity or chamber formed between the engaged dies through a sprue in the fixed die. Aluminium and copper alloys which attack and erode machine parts with which they are in constant contact are usually made in a so-called cold chamber machine, whilst tin, lead and zinc die castings are usually produced in a so-called hot chamber machine. Our invention can equally well be utilised on hot chamber and cold chamber pressure die casting machines, though for simplicity only a hot chamber machine is discussed below. DISCLOSURE OF THE PRIOR ART An hydraulic cylinder unit for die actuation is disclosed in British Patent 1,371,199 (Hehl), but with the dies mounted directly on the piston rods. Thus there is no disclosure of a die-casting machine, with platens. STATEMENT OF THE INVENTION According to one feature of the invention we provide a die ' casting machine which includes in combination a machine base; a first platen fixed to the machine base; a second platen fixed to the machine base; a third platen movable relative to the machine base, and positioned between the first and second said platens; means removably to mount first and second die parts respectively to said first and third platens; at least two tie bars connecting the first and second platens and adapted to inhibit separation of the first and second platens during die casting, the third platen being slidably mounted on said tie bars; a protrubrance on each said tie bar, the tie bar having a smaller diameter to one side of the protrubrance than to the other side thereof; tie bar hydraulic cylinders connected to the third platen and each slidable sealingly upon a respective protrubrance whereby said protrubrance forms a stationary piston defining first and second hydraulic chambers within the movable hydraulic cylinder; at least two guide bars connected to the first platen and projecting through the third platen, each said guide bar having a guide bar protrubrance; guide bar hydraulic cylinders connected to the third platen and each slidable sealingly upon a respective guide bar protrubrance whereby said protrubrance forms a stationary piston defining first and second hydraulic chambers within the movable hydraulic cylinder; and first and second hydraulic conduit means connected respectively to the first and second hydraulic cylinder chambers for movement of the cylinder and thus of the third platen in opposite respective directions. Preferably the first chambers of the tie bar cylinders and of the guide bar cylinders are of equal hydraulic cross section. Thus usefully the tie bar and guide bar cylinders are of equal diameter, and each guide bar is of equal diameter to each tie rod. In a preferred arrangement the first and second hydraulic chambers of a hydraulic cylinder are interconnected through a regeneration or transfer valve, one valve for each cylinder; the regeneration valve can be closed to prevent hydraulic connection between the two chambers, whereby the first chamber of each hydraulic cylinder can be used to clamp first and second die parts mounted to the first and third platens tightly together. The hydraulic conduit means can include first and second shuttle valves connected simultaneously to the pressure supply and to reservoir, the first shuttle valve being a three-position valve and the second shuttle valve being a two-position valve. Thus the three position valve can have a mid-position preventing pressure flow to one of the tie bar and guide bar cylinder chambers and exhaust flow to reservoir from the other of the tie bar and guide bar cylinder chambers, and furthermore can have first and second end positions respectively controlling hydraulic flow to the tie bar and guide bar cylinder chambers, the separate cylinder sets being one for die closing and one for die opening movement. Furthermore the second shuttle valve can have a first end position for connecting pressure supply to first hydraulic lines to the tie bar and guide bar cylinders, one way valves in said hydraulic lines downstream of the said second shuttle valve preventing pressure supply to said cylinders, and the second shuttle valve can have a second end position connecting pressure supply to second hydraulic lines to the said cylinders and to a dedicated regeneration valve for each cylinder whereby to close the regeneration valve to prevent interconnection of the cylinder first and second chambers so that all cylinders have a chamber at supply pressure and participate in clamping of the first die part to the second die part. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be further described by way of example with reference to the accompanying drawings, in which :- Fig.l is a schematic representation of a die casting machine according to the invention; Fig.2 is representation of part of the hydraulic circuit for the machine of Fig.l, used in the die opening condition; Fig.3 is a representation of another part of the hydraulic circuit of Fig.2, used in the die closing condition; Fig.4 is a representation of a further part of the hydraulic circuit of Fig.2, used in the die clamping condition; Fig.5 is a schematic representation of another embodiment of die casting machine according to the invention; Fig.6 is a representation of a part of the hydraulic circuit for the machine of Fig.5, similar to the representation of Fig.4; and Fig.7 is a representation of another part of the hydraulic circuit of Fig.6. DESCRIPTION OF EXEMPLARY EMBODIMENT In the figures, parts which perform the same or similar function carry the same reference numerals. The die casting machine 1 comprises a first platen 10 and a second platen 12, which are both fixed to a machine base (not shown), and a third platen 14 which is movable towards and away from the fixed first platen 10. Facing dies (not shown) will be removably mounted to the fixed and movable platens 10,14, in a manner known in the art, so that they can be replaced when worn or when a different product is to be die-cast. Two hydraulic cylinders 20,30 are shown, one end of each being connected to the movable platen 14. Hydraulic cylinder 20 is a tie bar hydraulic cylinder, i.e. its protuberance or piston 21 has secured to its opposite sides one end of each of first and second tie bar parts 22 and 23. First tie bar part 22 has its opposed end fixed to the first platen 10; second tie bar part 23 has its opposed end fixed to second platen 12. Hydraulic cylinder 30 is a guide bar hydraulic cylinder, i.e. its protuberance or piston 31 is mounted to one end of the guide bar 32, the other end of guide bar 32 is fixed to the first platen 10. Affixed to the guide bar hydraulic cylinder 30 is a tail 33, slidably received in an aperture 34 of second platen 12. Guide bar 32 has the same cross sectional area as first tie bar part 22. In the preferred embodiment there will be matched pairs of hydraulic cylinders 20,30, with one of each pair adjacent diametrically opposed corners of movable platen 14 and the other of each pair adjacent the other diametrically opposed corners. In alternative embodiments there can be more than four hydraulic cylinders, but mounted for balanced loading of the platens and dies. Piston 21 divides the tie bar hydraulic cylinder 20 into first chamber 25 and second chamber 26. The chambers 25,26 can be interconnected by way of hydraulic line 27 through a transfer or regeneration valve 28; or can be disconnected when valve member 29 is forced against its seat (downwardly as drawn) by hydraulic pressure in line 40. As shown, first tie bar part 22 is of smaller section than second tie bar part 23 so that first chamber 25 is of larger annulus than second chamber 26. Piston 31 divides the guide bar hydraulic cylinder 30 into a first hydraulic chamber 35 and a second hydraulic chamber 36. The first hydraulic chamber 35 is of smaller annulus than the effective section of second chamber 36. The chambers 35,36 can be connected by hydraulic line 37 through a transfer or regeneration valve 38; or can be disconnected when valve member 39 is forced against its seat (upwardly as drawn) by hydraulic pressure in line 40. As can be seen from Fig.l hydraulic pressure acts in lines 40 and 41 together. Line 41 is in communication with first chambers 25,35, by way of check valves 42,43 and transfer valves 28,38 respectively, for a purpose to be described below. Hydraulic lines 40,41 lead from, two-position shuttle valve 50, as does hydraulic line 45. In the right-hand position of shuttle valve 50 shown in Fig.l, lines 40,41 are connected to reservoir tank T, whilst line 45 is connected to pump P. The hydraulic circuit of Fig.l also contains a three- position shuttle valve 52, controlling hydraulic lines 54,55. Line 54 is in communication with the tie bar hydraulic cylinder 20; line 55 is in communication with guide bar hydraulic cylinder 30. In the position shown in Fig.l, lines 54,55 are disconnected from pump P and tank T, and are also isolated from line 45 by respective check valves 46,47. Thus Fig.l is of the system condition when not in a die-casting mode, with pump P inoperative so that the hydraulic lines 40,41,54,55 are not under pressure. For convenience, lines under hydraulic pressure are shown in Figs 2-4,6 and 7 by long/short symbols, whilst lines under reservoir pressure are shown by dotted symbols. Fig.2 shows three-position shuttle valve 52 moved to its right hand end position. In this position pressure from pump P is fed to line 55 and thus to second chamber(s) 36 of guide bar hydraulic cylinder(s) 30, whilst line 54 from tie bar cylinder(s) second chamber 26 is connected to tank. In this figure, line 40 is unpressurised, so that the valve member 39 can be lifted from its seat, allowing hydraulic fluid to flow between the first and second guide bar cylinder chambers 35,36. Hydraulic pressure from line 55 acts directly in chamber 36, and by way of transfer valve 38 and line 37, this same pressure acts indirectly upon guide bar cyclinder first chamber 35; because of the differential hydraulic area the cylinder 30 is forced to the left as viewed, the excess fluid in the first chamber 35 being forced into the second chamber 36 to supplement the fluid being introduced through line 55. Thus, there is caused the withdrawal of the platen 14 from fixed platen 10 whereby to open the fitted die faces for ejection of the cast product. - li ¬ lt will be understood that the check valve 43 prevents pressure escape to line 41. It will also be understood that fluid forced out of the first chamber 25 of the tie bar cylinder 20 will pass along line 27, through transfer valve 28 into tie bar cylinder second chamber 26; part of this fluid will occupy the increase in volume of the second chamber 26 as the platen 14 moves, but the excess will pass through the conduit in the second tie bar part 23, into line 54 and out to the tank T. Thus, the hydraulic fluid displaced from the first chamber 35 into second chamber 36 of the guide bar cylinder limits the volume of top-up fluid required from pump P, saving both on pump energy and volume, and giving the potential for shorter cycle times i.e. increased cast product output from between the dies. For subsequent die closure, the three-position shuttle valve 52 is moved to the left hand position, as shown in Fig.3. In this position of the valve 52 the pump P is connected to line 54, whilst line 55 is connected to tank T. Line 54 feeds fluid under pressure directly to tie bar cylinder second chamber 26, and by way of transfer valve 28 and line 27 to tie bar cylinder first chamber 25. With chambers 25,26 pressurised, the differential hydraulic area to either side of piston 21 causes the cylinder to be forced to the right as viewed, moving the third platen 14 closer to the first platen 10, and closing the mould. The excess fluid in the second chamber 26 is forced into the first chamber 25, to supplement the fluid being introduced through line 54 and line 27. It will be understood that in this mode of operation the check valve 42 prevents pressure escape to line 41. It will also be understood that some of the fluid forced out of the second chamber 36 of the guide bar cylinder 30 will pass through transfer valve 38 along line 37 and into first chamber 35 to occupy the increase in volume of the first chamber as the platen 14 moves, but the remainder or excess will pass through the conduit in the tail 32, into line 55 and out to the tank T. Thus, on closing the mould, the hydraulic fluid displaced from the tie bar cylinder second chamber 26 into first chamber 25 limits the volume of top-up fluid required from pump P, again saving both on pump energy and volume and giving the potential for shorter cycle times. The use of fluid from one chamber being introduced to another chamber to supplement that provided by the pump is known as regeneration; we are thus able to provide regeneration in both the opening and closing modes of operation. The selection of the relative diameters of the first and second tie bar parts 22,23, of the guide bar 32, and of the cylinders 20,30, will allow the choice of the speed of opening/closing for a given pump displacement, by determining the amount of regeneration in each direction. For die clamping, with the mould closed i.e. the die faces in tight abutment to prevent the escape of molten die material, the circuit positions shown in Fig.4 are used. The three-position valve 52 is moved to its central position, whilst the two-position valve 50 is moved to its left-hand end position; in this position of valve 50 the pump P is connected to lines 40,41, whilst lines 54,55 from second chambers 26,36 are connected to tank T by way of check valves 46,47 and line 45. The pressure in line 40 causes the valve members 29,39 to engage their respective seats, so that the line 41 is in communication with both of first chambers 25,35 but not in communication with second chambers 26,36 (the hydraulic fluid can pass around the annular boss of valve members 29,39). Thus in this embodiment all of the first chambers are under an identical hydraulic pressure, providing balanced clamping across the platen 14. In another, less preferred embodiment, the clamping is provided by only some of the first chambers, such as two diagonally opposed chambers of a machine with four hydraulic cylinders. Usefully the pump P is a double displacement pump, permitting fast, low pressure hydraulic flow for platen 14 retraction (Fig.2) and advance (Fig.3), but a slow, high pressure flow for platen clamping (Fig.4). A particular advantage of our arrangement is the facility provided for rapid die replacement. For known machines, typically, the dies are mounted to the platens between the tie bars, the dies having recesses to accommodate the tie bars. To remove such a die, particularly a larger die, it is usually necessary to remove one of the tie bars, which may involve the mechanical uncoupling of the tie bar(s). For such a die replacement we now propose hydraulically to withdraw one of the guide bars, preferably an upper one. Since the guide bar is connected to the machine at one of its ends only, the (mechanical) disconnection of this end will permit it hydraulically to be slid back into its cylinder, to provide a "passageway" allowing subsequent removal of the die. Thus the movable platen 14 is mechanically locked against movement, and the upper of the matched pair of diametrically opposed guide bars 32 is uncoupled from the fixed platen 10; shuttle valve 50 is moved to its left hand position so that pressure can then be applied through line 41, to move piston 31 (and thus guide bar 32) to the left as viewed in Fig.l until piston 31 abuts the rear wall of cylinder 30. In the embodiment of Fig.6, two further valves 60 and 62 are added to the hydraulic circuit. In this embodiment the valves 60,62 are solenoid valves. Also, in this embodiment, the tank T and pump P connections to valve 52 are reversed, for simplicity. Thus in the embodiment of Fig.6, the lines 40 and 41 are separated, for separate pressurisation. Thus, the pressurising of line 40, operative to close the regeneration valves 28,29 (to prevent regeneration) is controlled directly by (solenoid) valve 60; the pressure in line 41 which provides the fluid pressure to clamp the dies is controlled directly by (solenoid) valve 50. When both valves 50 and 60 are in the positions shown in Fig.6, both of lines 40 and 41 are (independently) pressurised, and so act to provide a balanced clamping force in each first chamber 25,26, as described in relation to Fig.4. Furthermore, valve 62 is now used to control the hydraulic retraction of a (or each) guide bar 32, to permit die replacement (as previously described). Thus when the die is open and the selected guide bar 32 has been mechanically released from the fixed platen 10, the valve 62 is moved to the position shown in Fig.7; the hydraulic fluid can now be placed under pressure in line 64, acting through valve 38 and in the first chamber 36 of the guide bar cylinder (not shown in this figure). As previously described, this causes the released guide bar to be retracted away from the fixed platen 10, permitting straightforward die removal and replacement. Thus, since in the embodiment of Fig.6 the line 41 is not pressurised during guide bar retraction, it is not necessary to lock the movable platen 14 against movement; pressurised fluid is introduced only into the first chamber of the guide bar which is to be retracted. As also shown for the valve positions of Fig.7, line 40 is pressurised, so that the valve 38 inhibits the flow of hydraulic fluid into the guide bar cylinder second chamber 36. When it is desired to reconnect the guide bar 32 with the fixed platen 10, valve 60 is moved to its other (right hand end) position, so that the regeneration valve 38 is released; fluid from line 64 may then flow into second guide bar cylinders 36, whereupon the different effective area in the first 35 and second 36 chambers causes the guide bar to be moved to the right i.e. towards the fixed platen 10, ready for reconnection.

Claims: CLAIMS Die casting machine characterised in combination by a machine base; a first platen (10) fixed to the machine base; a second platen (12) fixed to the machine base; a third platen (14) movable relative to the machine base, and positioned between the first and second said platens; means removably to mount first and second die parts respectively to facing surfaces of said first and third platens; at least two tie bars (22,23) connecting the first and second platens and adapted to inhibit separation of the first and second platens during die casting, the third platen being slidably mounted on said tie bars; a protrubrance (21) on each said tie bar and located between the second and third platens, the tie bar having a smaller diameter to the side of the protrubrance connected to the first platen than to the other side thereof; tie bar hydraulic cylinders (20) connected to the third platen and each slidable sealingly upon a respective protrubrance whereby said protrubrance forms a stationary piston defining first and second tie bar hydraulic chambers (25,26) within the movable hydraulic cylinder; at least two guide bars (32) connected to the first platen and projecting through the third platen, each said guide bar having a guide bar protrubrance (31) located between the second and third platens; guide bar hydraulic cylinders (30) connected to the third platen and each slidable sealingly upon a respective guide bar protrubrance whereby said protrubrance forms a stationary piston defining first and second guide bar hydraulic chambers (35,36) within the movable hydraulic cylinder; and first and second hydraulic conduit means (P,T,27,37,54,55) connected respectively to the first and second hydraulic cylinder chambers. 2. Die casting machine characterised in combination by a machine base; a first platen (10) fixed to the machine base; a second platen (12) fixed to the machine base; a third platen (14) movable relative to the machine base, and positioned between the first and second said platens; means removably to mount first and second die parts respectively to facing surfaces of said first and third platens; at least two tie bars (22,23) adapted to inhibit separation of the first and second platens during die casting, the third platen being slidably mounted on said tie bars; a protrubrance (21) on each said tie bar; tie bar hydraulic cylinders (20) connected to the third platen and each slidable sealingly upon a respective protrubrance whereby said protrubrance forms a stationary piston defining first and second hydraulic chambers (25,26) within the movable hydraulic cylinder; at least two guide bars (32) projecting through the third platen, each said guide bar having a guide bar protrubrance (31); guide bar hydraulic cylinders (30) connected to the third platen and each slidable sealingly upon a respective guide bar protrubrance whereby said protrubrance forms a stationary piston defining first and second hydraulic chambers (35,36) within the movable hydraulic cylinder; and first and second hydraulic conduit means (27,37,54,55) connected respectively to the first and second hydraulic cylinder chambers whereby to permit pressurised movement of the cylinder and thus of the third platen in opposite respective directions; each tie bar being fixed both to the first and second platens, each guide bar being fixed only to the first platen and not to the second platen. 3. A die casting machine according to claim 2 characterised in that at least one tie bar has a smaller diameter to the side of its protrubrance (21) facing the first platen (10) than to the other side thereof, and in that at least one guide bar (32) terminates at its protrubrance (31). 4. A die casting machine according to claim 1 or claim 3 characterised in that a first regeneration valve (28) is connected between the first and second chambers (25,26) of the tie bar hydraulic cylinder (20) and a second regeneration valve is connected between the first and second chambers (35,36) of the guide bar hydraulic cylinder (30). 5. A die casting machine according to any of claims 1-4 characterised in that each guide bar hydraulic cylinder (30) has a tail (33), the tail being slidably received in an aperture (34) of the second platen. 6. A die casting machine according to any of claims 1-5 characterised in that at least one guide bar (32) is releasably fixed to the first platen (10). 7. A die casting machine according to any of claims 1-6 characterised in that the hydraulic conduit means includes first valve means (52), the said valve means having a first position in which the guide bar cylinder second chamber (36) is connected to a pump (P) and the tie bar cylinder second chamber (26) is connected to a reservoir (R), the valve means having a second position in which the guide bar cylinder second chamber (36) is connected to the reservoir (R) and the tie bar cylinder second chamber (26) is connected to the pump (P) . 8. A die casting machine according to claim 7 characterised in that first valve means has a third position in which the valve means disconnects the said second chambers (26,36) from both the reservoir (R) and the pump (P) , and in that the hydraulic circuit includes second valve means (50), the second valve means being effective for supplying fluid to each of the first chambers (25,26) concurrently to provide a balanced clamping force across the third platen (14). 9. A die casting machine according to claim 8 characterised in that the hydraulic circuit includes third valve means (62), the third valve means being effective for supplying fluid to the guide bar first chamber (35) to provide a force for retracting said guide bar. 10. A die casting machine according to any of claims 1-9 characterised in that the said first chambers (25,35) are of equal hydraulic cross section and in that the said hydraulic cylinders (20,30) are of equal diameter.

Inventors: HARRISON PETER, HARRISON, PETER
Applicants: HARRISON PETER, REDMAN E M B LTD, E.M.B.-REDMAN LIMITED, HARRISON, PETER
Application year: 1994
Main classification: B29C45
IPC codes: B22D17, B29C45